1. Field of the Invention
The present invention relates to a successive vapor deposition system suitable for successive formation of thin layers of different vapor deposition materials onto a substrate. The present invention also relates to a vapor deposition system and a vapor deposition process.
2. Description of the Related Art
A typical organic electroluminescent device generally has a hole-transporting layer, a luminescent layer, an electron-transporting layer and an electrode layer which are formed by vacuum deposition successively on an ITO (Indium tin oxide) glass substrate. In conventional successive vapor deposition systems for forming such successive layers on the glass substrate, a plurality of vacuum deposition chambers (which include a substrate stock chamber and a preliminary treatment chamber) for evaporating different vapor deposition materials onto the glass substrate are arranged radially with respect to a central vacuum carrier robotic chamber, so that the glass substrate is successively transferred from one chamber to another among the plurality of vacuum deposition chambers via a robotic system of the central vacuum carrier robotic chamber to form thin layers of the different materials on the glass substrate.
In such conventional successive vapor deposition systems, the substrate needs to be successively displaced from one chamber to another, among the plurality of vacuum deposition chambers, via the central vacuum carrier robotic chamber, which is a time-consuming and inefficient operation. In addition, vapor deposition materials are consumed excessively because of the fundamental structure of the conventional systems in which vacuum deposition chambers are merely arranged around the central vacuum carrier robotic chamber. Specifically, in such conventional successive vapor deposition systems, different vapor deposition materials and the substrate are respectively arranged on lower and upper areas in a vacuum deposition chamber, and the different vapor deposition materials are heated to be vaporized (or sublimed) while the substrate is being rotated on its axis or revolved around the axis of the central vacuum carrier robotic chamber to form layers of the different vapor deposition materials entirely on one side of the substrate with a substantially even layer thickness. However, an excessive consumption of the vapor deposition materials cannot be avoided because the evenness of the layers is ensured only by depositing a portion of vaporized molecules onto the substrate, the vaporized molecules of which are spread out widely upwards in all directions from crucibles or boats, each of which is approximately regarded as a point source of evaporation. In other words, an excessive consumption of the vapor deposition materials cannot be avoided because most of the vaporized molecules are deposited onto inner walls of the vacuum deposition chambers; only a few percent of the vaporized molecules is deposited onto the substrate in practice. Some vapor deposition materials used in production of organic electroluminescent devices are extremely expensive, e.g., tens of thousands of yen per gram. Accordingly, an excessive consumption of the vapor deposition materials causes a substantial increase in the cost of production.
In an organic electroluminescent device, a host material and at least one dopant material are generally co-deposited on the substrate at a specific ratio (e.g., a ratio of 100 to 1, or a ratio of 100 to 0.5) in order to determine the luminescent color of an organic luminescent layer. However, in conventional organic electro-luminescent devices, most of such different materials are wasted, and further, it becomes difficult to retain the specific ratio over time.